Introduction

This chapter considers (a) the generation of highly branched (colonial)mutants during prolonged fermentation of the Quorn® myco-protein fungus, Fusarium graminearum A3/5, (b) the influence of hyphal branch frequency on the production of extracellular enzymes by Aspergillus oryzae, and (c) the stability of Aspergillus niger gla A transformants in prolonged continuous how cultures. We believe that the results obtained with these three species can be extended to most, if not all, filamentous fungi.

Highly branched mutants do not have a selective advantage because of their morphology

When filamentous fungi or streptomycetes are grown in prolonged, continuous culture, it is common for the relatively sparsely branched parental strain to be supplanted by a relatively highly branched mutant (Fig. 5.1). Such mutants are called colonial because in Petri dish culture they form dense colonies that expand in radius more slowly than parentalcolonies. Selection of colonial mutants has been observed in continuouscultures of Byssochlamys nivea, Paecilomyces variotii, Paecilomyces puntanii, Gliocladium virens, Trichoderma viride (Forss et al., 1974), Penicillium chrysogerrum (Righelato, 1976), F. graminearum (Solomons & Scammell, 1976) and Acremonium chrysogemrm (A. Trilli, personal communication).